What does testosterone do for men?
It runs your sex drive, erections, sperm, muscle and bones. Treatment is for men who are truly low. And taking it can shut down the very sperm it helps you make.
On this page
What does testosterone do in a man’s body?
Testosterone is the main male hormone. Your testicles make it, on a signal from your brain. The British Society for Sexual Medicine (BSSM) says it is essential for building and keeping male features.
At puberty, the NHS lists these changes in boys: a larger penis and testicles, a deeper voice and hair in the armpits and groin.
| Part of the body | What testosterone does |
|---|---|
| Brain | Drives sex drive. Also plays a part in memory, thinking and feelings. |
| Penis | Helps erections work. |
| Testicles | Helps make sperm. |
| Muscle | Supports muscle size and strength. |
| Bones | Helps bones grow and stay dense. |
| Blood | Helps your body make red blood cells. |
| Skin and hair | Grows body hair and makes skin oilier. |
Source: BSSM
So when it runs low, the first signs are usually sexual. BSSM names the 3 most common: erection problems, losing morning erections and low sex drive.
Notice any of these? Read the full list of low testosterone symptoms in men before you book a test.
Does testosterone drop with age?
Yes, but slowly. The NHS says it falls by about 1% a year from around 30 to 40. On its own, that is unlikely to cause any problems.
Think of a slow puncture, not a blowout. On its own it rarely leaves you flat. Real problems usually have another cause.
Real deficiency is different. The NHS calls it uncommon and not a normal part of ageing. It is more likely if you are obese or have type 2 diabetes.
Tired, low and off sex in your 40s or 50s? The NHS says the cause is often not hormones at all. Stress, depression, poor sleep, drinking too much and smoking can all do it.
See testosterone levels by age and what causes low testosterone.
What are the benefits of testosterone treatment?
For men who are truly low, the clearest gain is sex. BSSM says treatment improves sexual desire, erections and satisfaction.
| Area | What trials found |
|---|---|
| Sex drive | Better. Desire can improve by 6 weeks. Erections may take longer. |
| Muscle and fat | More muscle, less fat. Weight and waist size didn’t change. |
| Mood | Slightly better, in men aged 65 and over. |
| Energy | No benefit, in men aged 65 and over. |
| Walking distance | No benefit, in men aged 65 and over. |
Sources: BSSM; T Trials (NEJM 2016)
The muscle and fat changes are slow. BSSM says they may take 12 months or more.
The energy result surprises people. In a year-long trial of 790 men aged 65 and over with low testosterone, testosterone gel gave no boost to energy.
Normal levels and want more muscle? Start with raising testosterone naturally and testosterone and muscle growth.
Who gets testosterone treatment in the UK?
You need two things: symptoms and low levels on two morning blood tests. BSSM uses total testosterone in nmol/L. Labs and guidelines vary, so ask what your lab’s range is.
- Below 8 nmol/LLow. Sex symptoms respond best here.
- 8 to just under 12 nmol/LUsually treated, if you have symptoms.
- 12 up to 14 nmol/LNot usually needed. A 6-month trial may suit some with symptoms.
- Above 14 nmol/LBSSM: treatment not needed.
Source: BSSM
Between 8 and 12? BSSM says to check free testosterone too, the part not attached to proteins in your blood, which your body can use. See free testosterone explained.
How a GP usually checks your testosterone
- 1
Talk first
Your GP asks about work, home life and stress.
- 2
Two tests
Between 7 and 11 am, ideally 4 weeks apart and, if possible, not while ill.
- 3
Specialist
A low result may mean a hormone specialist (endocrinologist).
- 4
Treatment
If confirmed, you may be offered a gel or an injection.
Testosterone is highest in the early morning, so timing matters. See the best time to test testosterone.
What are the side effects of testosterone?
Here is the catch from the top of the page. Testosterone from outside tells your brain to stop the signal to your testicles. Your own testosterone falls, and so does sperm making.
In younger men, treatment often causes infertility after 6 to 12 months. It reverses in 60% to 70% of men within 12 months of stopping. See the male fertility blood test.
Treatment can also thicken your blood by raising red blood cells. So BSSM advises regular blood checks.
What about your heart? One trial treated 5,246 men aged 45 to 80. All had low testosterone and heart disease, or a high risk of it.
Treatment caused no rise in heart attacks or strokes. But there was more irregular heartbeat, sudden kidney injury and blood clots in the lungs.
Before you start testosterone
- Tell your doctor if you want children. Testosterone can stop you making sperm.
- Ask which checks you’ll have, including a prostate blood test (PSA). BSSM advises them at 3 months, 6 to 12 months, then every year.
- Give it 6 months. If sex drive, sex function, muscle function or body fat show no benefit by then, BSSM says treatment should stop. Book a review with your prescriber to decide.
- Keep working on weight and lifestyle. BSSM advises this alongside treatment.
- Don’t take testosterone or other steroids without a prescription. The NHS says steroids are addictive and lists infertility, shrunken testicles, breast growth, heart attack and stroke.
Sources: BSSM; NHS: anabolic steroids
When to speak to a GP
Book an appointment if:
- Erection problems keep happening. The NHS says see a GP or a sexual health clinic.
- You’re worried about a low sex drive, or think a medicine, such as one for blood pressure or an antidepressant, is affecting it.
- You have low mood, loss of muscle, tiredness or poor sleep and want to find the cause. The NHS says see your GP.
- A boy shows no signs of puberty by 15. The NHS calls this possible delayed puberty.
- You think you’re addicted to anabolic steroids. The NHS says see a GP.
Never stop or change a prescribed medicine without your prescriber.